The present invention is set against a background of change in society's attitudes to how natural resources are used. Petroleum feedstocks are nonrenewable and increasingly costly, even impacting significantly on national balances of payment, and supply can be uncertain. There is a perception, increasingly commonly held, that it may be for the general good of society, as well as of the environment, to reduce the reliance of consumer disposable goods manufacturing on such feedstocks. However, a serious response to such notions requires efficient processes for converting locally or regionally available renewable resource feedstocks into desirable consumer goods such as laundry detergents.
The United States produces very considerable tonnages of sugars, such as glucose or corn syrup, as well as of fatty substances. There is a downward trend in traditional patterns of consumption of these particular renewable resources: people are tending to eat less sugars, and also less fatty foods, especially saturated fats, for health-related reasons. This makes their development for other uses, such as laundry detergents, all the more attractive.
A number of years ago, processes were explored for making textile assistants or detergents from fatty acids or their derivatives in combination with N-alkylglucamines, the latter made by reductive amination of glucose. Glucose reductive amination processes are more fully disclosed in U.S. Pat. No. 2,016,962, Flint et al, issued Oct. 8, 1935.
U.S. Pat. No. 1,985,424, Piggott, issued Dec. 25, 1934 discloses manufacturing "textile assistants" by reacting (a) the product of heating glucose and aqueous methylamine in presence of hydrogen and a hydrogenating catalyst under pressure with (b) an organic carboxylic acid such as stearic acid or oleic acid. The condensation product, prepared at about 160.degree. C., is said to be "predominantly, if not exclusively, an amide" and is assertedly of the formula R-CO-NR.sub.1 -CH.sub.2 -(CHOH).sub.4 -CH.sub.2 OH wherein R is an alkyl radical containing at least 3 carbon atoms, while R.sub.1 is hydrogen or an alkyl radical.
U.S. Pat. No. 2,703,798, Schwartz, issued Mar. 8, 1955 asserts that compositions produced by reacting fatty acids or acid anhydrides with N-alkylglucamines (presumably such as the process as taught by Piggott) have poor color and poor detergency properties. It is indeed chemically reasonable that more than one compound can be formed by the Piggott process. Piggott makes no attempt to quantitatively prove the structures of the compounds or mixtures he prepared.
Schwartz (U.S. Pat. No. '798) goes on to report an improvement as a result of reacting fatty ester (as distinct from fatty acid or anhydride) with N-alkylglucamines. Although this process may overcome one or another deficiency of the art, such as of Piggott, it now transpires that the Schwartz process still has difficulties, in particular, in that complex mixtures of compounds can be formed even by the Schwartz process. The reaction may take several hours and the process can fail to give high quality product. Neither the process of Piggott not the process of Schwartz is known to have ever borne fruit in commercial practice.
In more detail, Schwartz notes that only one of several possible chemical reactions takes place when N-monoalkylglucamines are condensed with fatty esters or oils. The reaction is said to give compounds formulated as amides, e.g., ##STR1## where R' is fatty alkyl and R is a short-chain alkyl, typically methyl. This structure is apparently the same as the structure proposed by Piggott. Schwartz contrasts the single-product outcome he believes he secures with compounds he asserts are actually produced when acids are reacted with N-alkylglucamines, namely mixtures of the amide (I) with one or more by-products, to which he assigns esteramide and esteramine structures and which assertedly include compounds which are "inert and waxy, impairing the surface activity of" the structure (I) amide.
According to Schwartz, approximately equimolar proportions of N-monoalkylglucamines can be reacted with fatty alkyl esters by heating at 140.degree. C.-230.degree. C., preferably 160.degree. C.-180.degree. C. at normal, reduced or superatmospheric pressures for a period "somewhat in excess of one hour" during which time two initially immiscible phases merge to form a product said to be a useful detergent.
Suitable N-monoalkylglucamines are illustrated by N-methylglucamine, N-ethylglucamine, N-isopropylglucamine and N-butylglucamine. Suitable fatty alkyl esters are illustrated by the product of reacting a C.sub.6 -C.sub.30 fatty acid with an aliphatic alcohol e.g., methyl ester of lauric acid. Mixed glycerides of Manila oil or mixed glycerides of cochin coconut oil can apparently also be used as the fatty ester. When the glucamine is N-methylglucamine, the corresponding products with these fatty esters are characterized as the "fatty acid amides of N-methylglucamine", which are useful detergent surfactants. Another specific composition reported is assertedly "N-isopropylglucamine coconut fatty acid amide".
U.S. Pat. No. 2,993,887, Zech, issued Jul. 25, 1961 reveals there is even more complexity to the reactions of fatty substances with N-methylglucamine. In particular, Zech asserts that the products of high-temperature reaction (180.degree. C.-200.degree. C.) within the range disclosed by Schwartz have cyclic structures. No fewer than four possible structures are given. See U.S. Pat. No. '887 at col. 1 line 63-col. 2 line 31.
What is now believed actually to be provided by the fatty ester- N-alkylglucamine process of Schwartz are compositions comprising mixtures of formula (I) compounds together with appreciable proportions (e.g., about 25%, often much more) of several other components, especially cyclic glucamide by-products (including but not limited to the structures proposed by Zech) or related derivatives such as esteramides wherein as compared with formula (I) at least one --OH moiety is esterified.
Moreover, a re-investigation of Schwartz suggests that there are other significant unsolved problems in the process, including a tendency to form trace materials imparting very unsatisfactory color and/or odor to the product. More recently, the work of Schwartz notwithstanding, Hildreth has asserted that compounds of formula (I) are new. See Blochem. J., 1982, Vol. 207, pages 363-366. In any event, these compositions are given a new name: "N-D-gluco-N-methylalkanamide detergents", and the acronym "MEGA". Hildreth provides a solvent-assisted process for making the compounds differing seminally from Schwartz in that it returns to the use of a fatty acid reactant, instead of fatty ester. Moreover, Hildreth relies on pyridiine/ethyl chloroformate as the solvent/activator. This process is specifically illustrated for octanoyl-N-methylglucamide ("OMEGA"), nonanoyl-N-methylglucamide ("MEGA-9") and decanoyl-N-methylglucamide ("MEGA-10"). The process is said to be cheap and high-yield. One must of course assume that "cheap" is relative and is meant in the sense of specialized biochemical applications of interest to the author: in terms of large-scale detergent manufacture, the use of pyridine and ethyl chloroformate would hardly be viewed as consistent with an economic or environmentally attractive process. Therefore, the Hildreth process is not further considered herein.
Hildreth and other workers have purified certain formula (I) compounds, e.g., by recrystallization, and have described the properties of some of the structure (I) compounds. Recrystallization is, of course, a costly and potentially hazardous (flammable solvents) step in itself, and large-scale detergent manufacture would be more economical and safer without it.
According to Schwartz supra, the products of the Schwartz process can be used for cleaning hard surfaces. According to Thomas Hedley & Co. Ltd. (now Procter & Gamble), British Patent 809,060 published Feb. 18, 1959, formula (I) compounds are useful as a surfactant for laundry detergents such as those having granular form. Hildreth (supra) mentions use of compounds of formula (I) in the biochemistry field as a detergent agent for solubilizing plasma membranes and EP-A 285,768, published Dec. 10, 1988 describes application of formula (I) compounds as a thickener. Thus, these compounds, or compositions containing them, can be highly desirable surfactants.
Yet another process for making compositions comprising formula (I) compounds is included in the above-identified disclosure of improved thickeners. See EP-A 285,768. See also H. Kelkenberg, Tenside Surfactants Detergents 25 (1988) 8-13, inter alia for additional disclosures of processes for making N-alkylglucamines which, along with the above-identified art-disclosed N-alkylglucamine processes can be combined with the instant process for an overall conversion of glucose and fatty materials to useful surfactant compositions.
The relevant disclosures of EP-A 285,768 include a brief statement to the effect that "it is known that the preparation of chemical compounds of formula (I) is done by reacting fatty acids or fatty acid esters in a melt with polyhydroxy alkylamines which can be N-substituted, optionally in the presence of alkaline catalysts". The above-referenced art strongly suggests that this statement is a gross simplification or is inaccurate. EP-A 285,768 does not cite any references i n support of the quoted statement, nor has any reference other than EP-A 285,768 been found which actually does disclose any catalytic condensation of N-alkylglucamines with fatty esters or fatty triglycerides.
The European Patent Application contains the following Example entitled "Preparation of N-methyl-coconut fatty acid glucamide" in which "Na methylate" is understood to be synonymous with "sodium methoxide" and which has been translated from the German:
"In a stirred flask 669 g (3.0 tool) of coconut fatty acid methyl ester and 585 g (3.0 tool) of N-methylglucamine with the addition of 3.3 g Na methylate were gradually heated to 135.degree. C. The methanol formed during the reaction was condensed under increasing vacuum at 100 to 15 mbar in a cooled collector. After the methanol evolution ended the reaction mixture was dissolved in 1.5 l of warm isopropanol, filtered and crystallized. After filtration and drying 882 g (=76% of theoretical) of waxy N-methyl coconut fatty acid glucamide was obtained. Softening point=80.degree. to 84.degree. C.; Base number: 4 rag. KOH/g."
EP-A 285,768 continues with the following:
"In a similar manner the following fatty acid glucamides were prepared:
______________________________________ Softening Base No. Yield Point (mg. % (.degree.C.) KOH/g) ______________________________________ N-methyl lauric acid glucamide 76 94-96 6 N-methyl myristic acid glucamide 75 98-100 3 N-methyl palmitic acid glucamide 75 103-105 5 N-methyl stearic acid glucamide 84 96-98 6" ______________________________________
To summarize some important points of what can be gleaned from the art, the aforementioned Schwartz patent teaches that the problem of making formula (I) compounds from fatty esters or triglycerides and an N-alkylglucamine is solved by selecting fatty ester (instead of fatty acid) as the fatty reactant, and by doing simple uncatalyzed condensations. Later literature, such as Hildreth, changes direction back to a fatty acid-type synthesis, but does not document either that the teaching of the Schwartz patent is in error or how, short of making highly pure formula (I) compounds, to make such surfactants to detergent formulator's specifications. On the other hand, there has been one disclosure, in a totally different technical field, of sodium methoxide-catalyzed formula (I) compound synthesis. As noted, the procedure involves gradual temperature staging up to 135.degree. C. and recrystallizing the product.
In view of the foregoing observations, it would be very desirable to further improve processes for making surfactant compositions comprising formula (I) compounds. Such processes should be useful on a large scale and should result directly in compositions meeting laundry detergent formulators' specifications without need for recrystallization.
Accordingly, it is an object of the instant invention to provide an improved catalyzed process for manufacturing surfactant compositions by reacting fatty esters and N-alkylglucamines in the presence of particular catalysts at elevated levels.
It is a further object to provide product compositions of the invention for use in laundry detergents, including not only linear glucamide surfactant compositions having excellent quality and color, but also compositions comprising the linear glucamide surfactant in combination with one or more solid-form alkaline laundry detergent builders such as sodium carbonate.
These and other objects are secured, as will be seen from the following disclosure.
SUMMARY OF THE INVENTION
The present invention relates to an improved process for preparing detergent surfactants, more specifically, surfactant compositions having a high proportion of compounds of formula (I) to wherein R' is fatty alkyl and R is a short-chain hydrocarbyl, typically methyl, ethyl or the like. Products of the invention include the detergent surfactant, as well as detergent compositions consisting essentially of mixtures of the surfactant with one or more additional laundry-useful components, especially alkaline laundry detergent builders.
In general, the process involves reacting fatty esters and N-alkylglucamines in the presence of particular catalysts at elevated levels.
Catalysts suitable for use herein are selected from the group consisting of trilithium phosphate, trisodium phosphate, tripotassium phosphate, tetrasodium pyrophosphate, tetrapotassium pyrophosphate, pentasodium tripolyphosphate, pentapotassium tripolyphosphate, lithium carbonate, sodium carbonate, potassium carbonate, disodium tartrate, dipotassium tartrate, sodium potassium tartrate, trisodium citrate, tripotassium citrate, sodium basic silicates, potassium basic silicates, sodium basic aluminosilicates, potassium basic aluminosilicates and mixtures thereof.
Most preferred catalysts include sodium carbonate, tetrasodium pyrophosphate, sodium basic aluminosilicates, sodium basic silicates and mixtures thereof.
The process efficiently converts the N-alkylglucamine, e.g., N-methyl-D-glucamine, to linear glucamide surfactant of quality suitable for the laundry detergent formulator, without need for recrystallization.
In a preferred embodiment, the invention encompasses a process wherein the catalyst is selected from the group consisting of sodium carbonate, potassium carbonate and mixtures thereof, the amount of said catalyst is from about 10 weight % to about 95 weight % based on the sum of the reactants, conversion of N-alkylglucamine to compounds having linear structure of formula ##STR2## wherein R is the alkyl residue of the glucamine and R' is the residue of the fatty ester is about 70 mole % or higher on N-alkylglucamine, and conversion of N-alkylglucamine to cyclic glucamide or esteramide by-products is about 15 mole % or lower.
The present catalysts, as they operate in the process, have the advantage of not catalytically increasing the formation of by-product such as esteramide or cyclized glucamide at the same time as catalyzing the desired amidation reaction. This is surprising since esteramide by-product formation is an esterification reaction, and catalysts such as sodium carbonate or potassium carbonate have heretofore been used for catalyzing esterification reactions. See, for example, U.S. Pat. No. 2,999,858, Curtis, issued Sep. 12, 1961 which discloses a conversion of sucrose to sucrose fatty esters. See also U.S. Pat. No. 3,558,597, von Brachel et al, issued Jan. 26, 1971.
In short, the present invention is surprising in its ability to catalytically form surfactant compositions rich in formula (I) compounds selectively, without at the same time catalytically increasing by-product formation, especially by esterification.
In general, the present process takes N-alkylglucamines to linear glucamides of formula (I) with a conversion of about 70 mole % or higher, more preferably 80 mole % or higher based on N-alkylglucamine, whereas the conversion of N-alkylglucamine to by-product having cyclic glucamide or esteramide structure is generally about 15 mole % or lower.
The N-alkylglucamine starting-material can be prepared by any of the above-referenced literature methods and is illustrated by N-methylglucamine, N-ethylglucamine, N-propylglucamine and N-butylglucamine.
Highly preferred fatty ester is selected from saturated fatty methyl esters and fatty triglycerides.
The N-alkylglucamine and fatty ester are preferably used in approximately equimolar proportions in terms of the number of moles of fatty carbonyl moieties of the fatty ester per mole of N-alkylglucamine. Excellent results can also be achieved when there is a slight excess of fatty ester, e.g., about 1.10 moles per mole of N-alkylglucamine. A slight excess of N-alkylglucamine can also be used.
The present invention has many advantages including a generally rapid and efficient process achieving a product which is useful without further purification for formulation in laundry detergents. The product of the process generally has good color and only low levels of nonvolatile by-product (notably cyclic by-product but al so esteramides and the like). In certain embodiments of the invention, novel and useful compositions such as surfactant/builder intermediates for the formulator of granular laundry detergents are also secured.
Percentages and proportions herein are normally designated on a mole percentage basis unless otherwise indicated.